The invention relates to a valve for the metered admixture of fuel, volatilized from the fuel tank of an internal combustion engine, to a fuel-air mixture supplied to the engine via an intake manifold.
Under environmental protection laws in some countries, fuel that has volatilized in the fuel tank, that is, gasoline vapor, must not be vented into the open but instead must be burned by being fed into the engine. To this end, the vent neck of the fuel tank is connected to a reservoir filled with activated charcoal, which holds the volatilized fuel while the engine is stopped and then releases it again when the engine is running. To accomplish this, the reservoir communicates via an intake line with the engine intake manifold, where the fuel vapor is added to the fuel-air mixture. Because this can increase the exhaust emissions, the fuel vapor can be admixed only in certain operating states of the engine and in certain quantities. This is accomplished with the so-called tank bleeder valve, which is disposed in the intake line between the reservoir and the intake manifold and is opened and closed, preferably in clocked fashion, by an electronic control system as a function of the engine operating state and of the exhaust emissions measured by a lambda sensor.
In a known tank bleeder valve of this type (German patent document No. DE 35 19 292 A1), the valve closing element is embodied such that it opens the valve opening when the electromagnet is without current; that is, the seat valve is open when there is no current. Because of the opened seat valve, there is communication between the intake manifold and the reservoir holding the fuel vapor, which leads to "dieseling", that is, to the engine's running after its ignition is shut off.